CVE-2025-39673 ppp: fix race conditions in ppp_fill_forward_path
A race condition in the Linux kernel PPP module can cause a system panic, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-39673?
CVE-2025-39673 is a critical vulnerability in Debian Debian Linux, published on 5 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ppp: fix race conditions in ppp_fill_forward_path
ppp_fill_forward_path() has two race conditions:
1. The ppp->channels list can change between list_empty() and list_first_entry(), as ppp_lock() is not held. If the only channel is deleted in ppp_disconnect_channel(), list_first_entry() may access an empty head or a freed entry, and trigger a panic.
2. pch->chan can be NULL. When ppp_unregister_channel() is called, pch->chan is set to NULL before pch is removed from ppp->channels.
Fix these by using a lockless RCU approach: - Use list_first_or_null_rcu() to safely test and access the first list entry. - Convert list modifications on ppp->channels to their RCU variants and add synchronize_net() after removal. - Check for a NULL pch->chan before dereferencing it.
Weakness: CWE-362
Which versions are affected by CVE-2025-39673?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-39673?
Apply the vendor's patch.
Is CVE-2025-39673 being exploited?
There is no known exploitation of CVE-2025-39673 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-67007, AZL-73647, BELL-CVE-2025-39673, DEBIAN-CVE-2025-39673, GHSA-xxf9-fpw2-6hgc, ROOT-OS-DEBIAN-12-CVE-2025-39673 and 4 more.